1. Field of the Invention
The present invention relates to a linear motion guide unit having wide application in sliding parts incorporated in, for example, assembling machines including semiconductor manufacturing equipments and so on, numerically controlled machine tools, measuring instruments, testing machines and the like. More particularly, it relates to a linear motion guide unit in which a slider is forced to move lengthwise along a track rail.
2. Description of the Prior Art
Linear motion guide units have been universally recognized for fundamental and versatile means to more encourage the recently remarkable growth of mechatronics. Although the linear motion guide units have been extensively built in machinery in fields as diverse as assembling machines including semiconductor manufacturing equipments and so on, numerically controlled machine tools, measuring instruments, testing machines and the like, the expansion of uses accompanied by the current developments in technologies requires more and more such linear motion guide units that can manage growing demands for high precision, low-frictional resistance, high-speed moving, easy assemblage, versatility and the like.
Conventionally, there is well known a linear motion guide unit of the sort disclosed in, for example Japanese Patent Laid-Open No. 2001-12465, which is a co-pending application filed by the present assignee. With the prior linear motion guide unit recited above, both the track rail and the slider are made on their sides with surfaces of reference, which are instrumental in setting the track rail and the slider on any machine bed and table, respectively, in their precise positions, keeping the working table against any deviation in position and any change in posture. The track rail is fixed to the machine bed with fastening bolts, with the side and bottom surfaces of reference coming into face-to-face abutment to their associated mating side and top surfaces of the machine bed, one to each mating surface, in their precise positions. The slider is also secured at a slider head thereof to the moving table with fastening bolts, with the side and upper surfaces of reference being brought into face-to-face engagement with their associated mating side and lower surfaces of the table, one to each mating surface, in their precise positions.
In a currently reality, moreover, the linear motion guide unit is expected to be less expensive, even with high precision. With the linear motion guide unit in which the track rail is made up of a pair of widthwise opposing sides and a bottom joined together to form an upward opened recess of U-shape in cross section as disclosed in Japanese Patent Laid-Open No. 2001-12465, the convexities bulged sidewise out of the sides of the track rail is small or narrow in width. This means that the track rail is unsteady in machining and, therefore, too troublesome in machining process to process it with accuracy.
Japanese Patent Laid-Open No. 11-30234, which is also another co-pending application of the present assignee, discloses a slide unit in which a recirculating-ball screw fits in a track rail of U-shape in cross section and an upper seal closes a clearance left between an upper face of a raceway groove on the slider and the track rail. With the prior slide unit recited just earlier, in which the track rail is composed of a pair of widthwise opposing sides and a bottom joined together to form an upward opened recess of U-shape in cross section, the track rail remains left coarse on its inside surface coming in sliding engagement with the lip of the upper seal mounted on the slider. This means it is very tough to move smoothly the slider, so that the sealing effect would be vulnerable.
Moreover, a track rail 40 as shown in FIG. 10 has been known for the linear motion guide unit. The track rail 40 is made up of a pair of side walls 43, 43 extending lengthwise in parallel with one another and a bottom 44 extending integrally with the side walls 43, 43. The track rail 40 is to be laid on a fixed base including machine beds and so on, with a lower surface 42 abutting against the fixed base, and fastened thereto. The side walls 43, 43 rise at right to the bottom 44 in a way their top faces 49 are in flush with each other. Between the sidewise opposing side walls 43, 43 of the guide rail 40 there is defined a guide channel 62 in which a slider will be accommodated for sliding travel lengthwise of the track rail 40. Sidewise outside surfaces 45 of the track rail 40 bulge out partly at 41, while inside surfaces 47 of the track rail 40 are made with raceway grooves 46, one to each inside surface. With the track rail 40 constructed as stated earlier, the bulged portions 41 above the sidewise outside surfaces 45 are each made to have a sidewise outermost face 48 that reaches in width HP less than a distance ranging from the lower surface 42 of the track rail 40 to the rail's center of gravity GP. That is to say, the sidewise outermost faces 48 on the bulged portions 41 are each formed to have the width HP that is curbed below the rail's center of gravity GP or made less than the height HGP of the center of gravity, which is measured from the lower surface 42 of the track rail 40 to the rail's center of gravity GP.
With the track rail 40 in which the sidewise outermost faces 48 of the bulged portions 41 are each made to have the width HP curbed below the height HGP of the center of gravity, measured from the lower surface 42 of the track rail 40 to the rail's center of gravity GP as stated earlier, now assuming the situation where the track rail 40 can not exempt from choosing, for example any one sidewise outermost face 48 on the bulged portions 41 for a surface of reference to fasten precisely the track rail 40 to the fixed bed. When the track rail 40 is laid down on a top plane 51 of a jig 50 in a fashion lying on the sidewise outermost face 48 of any one bulged portion 41 to come in contact with the top plane 51 of the jig 50, the top face 49 of the side wall 43 lying on the jig 50 leans downward against the top plane 51 because the sidewise outermost face 48 is too narrow or small. Eventually the track rail 40 would result in tilting θ degrees relatively to a plane normal to the top plane 51 of the jig 50. In order for the guide rail 40 to remain lying steady on the top plane 51 of the jig 50 in a vertical posture where the sidewise outermost face 48 of the bulged portion 41 is kept throughout in close engagement with the top plane 51 of the jig 50 without leaning away from the top plane 51, a different jig needs to be replaced for every track rail 40. The prior track rail 40, because of the sidewise outermost face 48 on the bulged portion 41 being small in width as stated earlier, is very tough to have the sidewise outermost face 48 on the bulged portion 41, which is precisely processed to make a just right angle or 90° with the lower surface 42 of the track rail 40. Thus, it has been much difficult so far to count on the sidewise outermost face 48 of the bulged portion 41 to provide the surface of reference, which could be mated with the fixed surface of reference on the machine bed.
For the linear motion guide unit compact or slim in construction in which the slider can travel relatively to the track rail with being less subjected to frictional resistance, thus, it has been expected to more quickly and precisely mount the worktable to the slider or mount the stationary bed to the track rail at a preselected mounting position and posture and further make certain that the slider and the track rail are kept at their mounting position and posture preselected with respect to, for example the worktable and the machine bed, respectively, even after a prolonged period of use.